The present invention relates to a signal transmission technology and, more particularly to an improvement in a method and apparatus for signal transmission employed in a connection approach for transmission and reception of a video signal, a trigger signal, and a control signal between a television camera for picking up an image, especially, a television camera used in a field of factory automation (FA), and a video apparatus for processing a signal of an image picked up by this television camera.
For example, in a manufacturing factory, there is a case where to in-situ monitor a size error etc. of a certain part being manufactured, a television camera (hereinafter referred to as camera) is movably mounted at a predetermined monitor position along a moving path of the part so that each time the part passes by in front of the camera it may be exposed for a predetermined lapse of time at a timing instructed from a separately installed video apparatus to perform image processing on thus obtained image data by using the video apparatus, thereby measuring a processed size of this part or displaying it on a display apparatus.
FIG. 8 is a conceptual diagram for showing a configuration example of a video system used in such a case. On the side of a camera, at an interface, first an analog video signal sent from the camera is converted into a digital signal of, for example, 10 bits, which is then time-division multiplexed on four pairs of (eight) signal lines in a transmission cable and transmitted as a serial signal to the side of a video apparatus. In this case, digital data is time-division multiplexed on the four pairs of signal lines at, for example, 1/7 of a period of a clock signal (which is transmitted from the camera side to the video apparatus side by using one pair of signal lines in the transmission cable), not shown, sent from the camera. The clock signal has a frequency of, for example, 30 MHz, so that one pixel of image data takes 1/30 MHz to be transmitted. From the video apparatus side, a variety of camera-bound control signals such as a signal for instructing exposure timing are transmitted to the camera side through four to five pairs of signal lines in the transmission cable. It is to be noted that in transmission of these signals in the cable, to improve noise tolerance, a non-inverted signal and an inverted signal are transmitted in a pair by using a signal system referred to as a low voltage differential signaling (LVDS).
As an interfacing scheme employed in such a video system as described above, a television camera connection referred to as Camera Link is known, which connection is described in a literature “Camera Link, Specifications of the Camera Link Interface Standard for Digital Cameras and Frame Grabbers”, October 2000. The disclosure of this literature is hereby incorporated by reference. According to “Camera Link” specifications, this Camera Link interface has three kinds of configurations of a base configuration, a medium configuration, and a full configuration as classified in accordance with image data quantity etc. of the camera. That is, since a single Channel Link chip is limited to 28 bits, some cameras may require several chips in order to transfer data efficiently, so that the following three kinds of configurations are prepared:    Base: 1 Channel Link Chip, 1 cable connector    Medium: 2 Channel Link chips, 2 cable connectors    Full: 3 Channel Link chips, 2 cable connectors